One example of a conventional refrigeration device that includes a vapor compression refrigeration circuit is an air conditioner that is employed to provide air conditioning for buildings or the like. This type of air conditioner primarily includes a heat source unit having a compressor and a heat source side heat exchanger, a plurality of user units having user side heat exchangers, and gas refrigerant connection lines and liquid refrigerant connection lines that connect these units.
With this air conditioner, each unit and the lines will be installed on site, and then during a test operation, the air conditioner will be charged with the amount of refrigerant needed in accordance with the length of the refrigerant connection lines. When this occurs, the decision as to whether or not the air conditioner has been charged with the required amount of refrigerant will be determined based upon the time needed for charging on site. This is because the length of the refrigerant connection lines will vary due to the site at which the air conditioner is installed. Because of this, the amount of refrigerant charged into the air conditioner must rely upon the charging task level.
One air conditioner that can solve this problem is a device which has a configuration that can detect when the liquid refrigerant stored inside a receiver provided in a refrigerant circuit reaches a predetermined liquid level, and can detect during refrigerant charging the amount of refrigerant that needs to be charged into the air conditioner. An air conditioner 901 having a configuration that can detect the liquid level of a receiver will be described below with reference to FIG. 10.
The air conditioner 901 includes a heat source unit 902, a plurality of (here, two) user units 5 that are connected in parallel, and a liquid refrigerant connection line 6 and a gas refrigerant connection line 7 that serve to connect the heat source unit 902 and the user units 5.
The user units 5 primarily include a user side expansion valve 51, and a user side heat exchanger 52. The user side expansion valve 51 is an electric expansion valve that is connected to the liquid side of the user side heat exchanger 52, and serves to adjust the refrigerant pressure, refrigerant flow rate and the like. The user side heat exchanger 52 is a cross fin tube type heat exchanger, and serves to exchange heat with indoor air. In the present embodiment, a user unit 5 includes a fan not shown in the figures) that takes in indoor air into the interior thereof, and serves to blow air outward, and is capable of exchanging heat between the indoor air and the refrigerant that flows in the user side heat exchanger 52.
The heat source unit 902 primarily includes a compressor 21, an oil separator 22, a four way switching value 23, a heat source side heat exchanger 24, a bridge circuit 25 that includes a heat source side expansion valve 25a, a receiver 26, a liquid side gate valve 27, and a gas side gate valve 28. The compressor 21 serves to compress refrigerant gas drawn therein. The oil separator 22 is arranged on the discharge side of the compressor 21, and is a vessel that serves to separate oil included in the refrigerant gas that has been compressed/discharged. The oil separated in the oil separator 22 is returned to the intake side of the compressor 21 via an oil return line 22a. The four way switching valve 23 serves to switch the direction of the refrigerant flow during switching between cooling operations and heating operations. During cooling operations, the four way switching valve 23 can connect the discharge port of the oil separator 22 and the gas side of the heat source side heat exchanger 24, and can connect the intake side of the compressor 21 and the gas refrigerant connection line 7. During heating operations, the four way switching valve 23 can connect the outlet of the oil separator 22 and the gas refrigerant connection line 7, and can connect the intake side of the compressor 21 and the gas side of the heat source side heat exchanger 24. The heat source side heat exchanger 24 is a cross fin tube type heat exchanger, and serves to exchange heat between air and refrigerant that acts as a heat source. The heat source unit 902 includes a fan (not shown in the figures) that takes in outdoor air into the interior thereof, and serves to blow air outward, and is capable of exchanging heat between the outdoor air and the refrigerant that flows in the heat source side heat exchanger 24.
The receiver 26 is, for example, a vertical type cylindrical vessel such as that shown in FIG. 11, and serves to temporarily store refrigerant liquid that flows in the main refrigerant circuit 10. The receiver 26 includes an intake port on the upper portion of the vessel, and a discharge port on the lower portion of the vessel. The bridge circuit 25 is formed from the heat source side expansion valve 25a and three check valves 25b, 25c, 25d, and serves to allow refrigerant to flow into the receiver 26 from the intake port of the receiver 26 and allow liquid refrigerant to flow out from the discharge port of the receiver 26, even when the refrigerant that flows in the main refrigerant circuit 10 flows into the receiver 26 from the heat source side heat exchanger 24 or flows into the receiver 26 from the user side heat exchangers 52. The heat source side expansion valve 25a is an electric expansion valve that is connected to the liquid side of the heat source side heat exchanger 24, and serves to adjust the refrigerant pressure, refrigerant flow rate and the like. The liquid side gate valve 27 and the gas side gate valve 28 are respectively connected to the liquid refrigerant connection line 6 and the gas refrigerant connection line 7. The main refrigerant circuit 10 of the air conditioner 901 is formed by these devices, lines, and valves.
Furthermore, the air conditioner 901 includes a liquid level detection circuit 930 that is connected to a predetermined position on the receiver 26. The liquid level detection circuit 930 is connected between the predetermined position of the receiver 26 and the intake side of the compressor 21, and can draw out refrigerant from the predetermined position of the receiver 26, reduce the pressure of the refrigerant, and return the refrigerant to the intake side of the compressor 21. Here, the predetermined position of the receiver 26 to which the liquid level detection circuit 930 is connected is a first predetermined position L1 (see FIG. 11) that corresponds to the amount of liquid refrigerant that is stored in the receiver 26 when the required amount of refrigerant is charged in the main refrigerant circuit 10. The liquid level detection circuit 930 includes a bypass circuit 931 having an open/close mechanism 931a composed of a solenoid valve and a pressure reduction mechanism 931b composed of a capillary tube that serves to reduce the pressure of refrigerant that is provided on the downstream side of the open/close mechanism 931a, and a temperature detection mechanism 932 composed of a thermistor that is arranged at a position on the downstream side of the pressure reduction mechanism 931b. 
The act of charging the main refrigerant circuit 10 of the aforementioned air conditioner 901 (which includes the receiver 26 and the liquid level detection circuit 930) with refrigerant (e.g., R407C) will be described.
First, the circuit configuration of the main refrigerant circuit 10 will be placed into cooling operation mode. During cooling operations, the four way switching valve 23 is in the state shown by the solid lines in FIG. 10, i.e., the discharge side of the compressor 21 is connected to the gas side of the heat source side heat exchanger 24, and the intake side of the compressor 21 is connected to the gas side of the user side heat exchangers 52. In addition, the liquid side gate valve 27, the gas side gate valve 28, and the heat source side expansion valve 25a are opened, and the aperture of the user side expansion valve 51 is adjusted so as to reduce the pressure of the refrigerant.
With the main refrigerant circuit 10 in this state, refrigerant will be charged into the main refrigerant circuit 10 from the exterior thereof, and a cooling operation will be performed. More specifically, when the heat source unit 902 fan, the user unit 5 fan, and the compressor 21 are actuated, gas refrigerant at a pressure Ps (about 0.6 MPa) (see point A in FIG. 12) will be taken into the compressor 21 and compressed to a pressure Pd (about 2.0 MPa, corresponding to a condensation temperature of 50° C. for the refrigerant in the heat source side heat exchanger 24). After this, the refrigerant will be sent to the oil separator 22 to separate the gas refrigerant and the oil (see point B in FIG. 12). After that, the compressed gas refrigerant is sent to the heat source side heat exchanger 24 via the four way switching valve 23, exchanges heat with outdoor air, and is condensed (see point C in FIG. 12). The condensed liquid refrigerant will be sent to the user units 5 via the bridge circuit 25 and the liquid refrigerant connection line 6. Then, the liquid refrigerant that is sent to the user units 5 is reduced in pressure by the user side expansion valve 51 (see point D in FIG. 12), and then exchanges heat with indoor air in the user side heat exchangers 52 and evaporated (see point A in FIG. 12). The evaporated gas refrigerant is again taken into the compressor 21 via the gas refrigerant connection line 7 and the four way switching valve 23. The same operation as the cooling operation is then performed.
Refrigerant will be charged into the main refrigerant circuit 10 while continuing this operation. Here, by controlling the flow rate of air blown by the fans of each unit 5, 902, only a portion of the total amount of refrigerant that is charged from the outside will be gradually stored as liquid refrigerant in the receiver 26, because the amount of evaporated refrigerant in the user side heat exchangers 52 will be balanced with the amount of condensed refrigerant in the heat source side heat exchanger 24.
Next, while the aforementioned refrigerant charging operation is performed, the open/close mechanism 931a of the liquid level detection circuit 930 will be open, a portion of the refrigerant will be drawn out from the first predetermined position L1 of the receiver 26, the pressure thereof will be reduced by means of the pressure reduction mechanism 931b, the temperature of the refrigerant after pressure reduction will be measured by means of the temperature detection mechanism 32, and then the refrigerant will be returned to the intake side of the compressor 21.
In the event that the amount of the liquid refrigerant stored in the receiver 26 is low, and the liquid level of the liquid refrigerant does not reach the first predetermined position L1 of the receiver 26, gas refrigerant in the saturated state (see point E of FIG. 13) will flow therein. This gas refrigerant will be reduced in pressure to pressure Ps by the pressure reduction mechanism 931b, and reduced in temperature from about 57° C. to about 20° C. (a temperature reduction of about 37° C.)(see point F of FIG. 13).
After this, when the liquid level of the liquid refrigerant reaches the first predetermined position L1 of the receiver 26 and liquid refrigerant in the saturated state in the receiver 26 flows into the liquid level detection circuit 930 (see point H of FIG. 13), by reducing the pressure of this liquid refrigerant to pressure Ps by means of the pressure reduction mechanism 931b, the temperature of the refrigerant will rapidly reduce from about 50° C. to about 3° C. (a temperature reduction of about 47° C.)(see point I of FIG. 13) due to the occurrence of flash evaporation.
Thus, in this air conditioner 901, a liquid level detection circuit 930 is provided which takes a portion of refrigerant out from the first predetermined position L1 of the receiver 26, reduces the pressure thereof, measures the refrigerant temperature, and then returns the refrigerant to the intake side of the compressor 21. Then, if the refrigerant taken out from the receiver 26 is in the gas state, the liquid level detection circuit 930 will reduce the temperature of the refrigerant reduced in pressure in the liquid level detection circuit 930 a small amount (from point E to point F of FIG. 13), and if the refrigerant taken out from the receiver 26 is in the liquid state, the liquid level detection circuit 930 will reduce the temperature of the refrigerant reduced in pressure by means of flash evaporation a large amount (from point H to point I of FIG. 13). If this temperature reduction is large, the liquid level detection circuit 930 will determine that the liquid refrigerant in the receiver 26 is stored up to the first predetermined position L1, and if this temperature reduction is small, the liquid level detection circuit 930 will detect that the required amount of refrigerant has been charged into the main refrigerant circuit 10 by determining that the liquid refrigerant in the receiver 26 has not been stored up to the first predetermined position L1. (e.g., refer to Japanese Patent Unexamined Publication No. 2002-350014)
However, there will be times in which the aforementioned conventional air conditioner 901 must be operated under conditions in which the temperature of the heat source (such as the outside air) of the heat source side heat exchanger 24 is high, and the refrigerant pressure on the discharge side of the compressor 21 is high. In addition, there will be times in which the operating refrigerant will be changed from R407C to R410A or the like having saturation pressure characteristics (i.e., a low boiling point) that are higher in pressure than R407C, R22, or the like.
For example, as shown in FIG. 14, when the operating refrigerant is changed to R410A, because the boiling point of R410A is lower than that of R407C, the condensation temperature of the refrigerant in the heat source side heat exchanger 24 during cooling operations is assumed to be the same 50° C. as when R407C is used, and the condensation pressure in the heat source side heat exchanger 24, i.e., the discharge pressure Pd′ of the compressor 21, is assumed to be about 3.0 MPa. Under these conditions, if the refrigeration cycle during cooling operations is drawn in FIG. 14, a line will connect points A′, B′, C′ and D′. Here, the point one must pay attention to is the inclination of the vapor line at point E′ at which the line segment B′-C′ intersects with the vapor line. As shown in FIGS. 12 and 13, when R407C is used as the operating refrigerant, the inclination of the vapor line at point E at which the line segment B-C intersects with the vapor line is approximately vertical with respect to the horizontal axis or inclined slightly to the right in the figures. However, as shown in FIG. 14, when R410A is used, the inclination of the vapor line at point E′ at which the line segment B′-C′ intersects with the vapor line is inclined to the left. Because of this, if one attempts to detect whether or not the refrigerant stored in the receiver 26 has reached a predetermined position by means of the liquid level detection circuit 930, then as shown in FIG. 13, if R407C is used the degree of temperature reduction when gas refrigerant in the saturated state is reduced in pressure (from point E to point F of FIG. 13) will be smaller than the degree of temperature reduction when liquid refrigerant in the saturated state is reduced in pressure (from point H to point I of FIG. 13). However, as shown in FIG. 15, if R410A is used, in order achieve the two-phase state when gas refrigerant in a saturated state is reduced in pressure (point E′ to point F′ of FIG. 15), the same temperature reduction will be produced as when flash evaporation occurs if liquid refrigerant in the saturated state is reduced in pressure (from point H′ to point I′ in FIG. 15). Note that with either refrigerant, a temperature reduction of about 47° C. (from 50° C. to 3° C.) will occur.
Because of this, even if the liquid level of the liquid refrigerant does not reach the first predetermined position L1 of the receiver 26, the sudden reduction in the temperature of the refrigerant taken from the first predetermined position L1 of the receiver 26 will be detected, and errors will occur in the determination of whether the liquid refrigerant is stored up to the first predetermined position L1 of the receiver 26.
In addition, this phenomenon is not limited only to situations in which the operating refrigerant is R410A. Even in situations in which R407C is used, the same phenomenon as with R410A will be produced if operations occur under conditions in which the outdoor air temperature is high and the condensation temperature of the refrigerant in the heat source side heat exchanger 24 is high, because the position of point E in FIGS. 12 and 13 will shift upward, and the inclination of the vapor phase will move leftward.